The present invention relates to the field of Insensitive Munitions (IM), and, more particularly, to a new and simplified mechanism for reducing the vulnerability of propellant loaded cartridges from unplanned thermal stimuli. The currently fielded LW30 mm ammunition requires improvement in insensitive munitions (IM) response without affecting structural and performance requirements. A novel cartridge case design was developed to meet all the system level requirements for LW30 mm ammunition. This design concept can also be implemented in other medium and large caliber munitions.
The primary objective of the present invention is that it meet the standards for an Insensitive Munition, i.e. passing the Fast Cook-Off (FCC)) and Slow Cook-Off (SCO) test requirements of MIL-STD-2105D. Further and significant objectives of the present invention which address the needs detailed above, include providing a means to vent centerfire medium and large caliber cartridges, without any weakness being created in the cartridge structure, without any mechanical device being added to the cartridge, without any significant change to the configuration or mass of the cartridge, and without adding any significant cost to the construction of the cartridge.
Confinement of energetic materials in medium caliber munition is a known aggravator of the reaction violence for gun propulsion systems, since the propellant burn rate varies as a power of the system pressure. Existing M788 and M789, 30 mm×113 mm Lightweight (LW30 mm) rounds are fired from the M230 cannon mounted on the AH-64 Apache and United States Special Operations Command (USSOCOM) Black Hawk helicopters. These munitions use a metal cartridge and are scored a Type-IV Insensitive Munitions (IM) response in Fast Cook-Off (FCO), Bullet Impact (BI), and Fragment Impact (FI) testing and are scored a Type-Ill in Slow Cook-Off (SCO). IM responses are scored by an Army Insensitive Munitions Board (AIMB), resulting in different levels: Type-I/II means Detonation/Partial Detonation; Type-Ill means Explosion; Type-1V means deflagration; Type-V means burning; and Type-VI means No reaction. Ammunition containers for all munitions are required to comply with Insensitive Munitions (IM) requirements set forth in MIL-STD-2105D. Regarding IM testing requirements, two tests may be used to simulate ammunition cartridges exposed to a fire, a slow cook off test (SCO) and a fast cook off test (FCO). In SCO, an ammunition container containing one or more munitions may be heated at a rate of 15 degrees F. per hour, as specified by STANAG 4382, until the munition reacts. In FCO, an ammunition container containing one or more munitions may be engulfed in a flame of at least 800° C. until the munition reacts. It may be desirable for the reaction to be limited to no more than burning (Type-V reaction). A detonation (Type-I reaction) may not be acceptable.
A fixed ammunition is an ammunition in which the cartridge case is permanently attached to the projectile. Such munitions include the LW30 mm, 30 mm×173 mm, 25 mm, 105 mm tank round, 105 mm artillery round, and etc.